The present invention relates to a processing system, a workpiece transfer mechanism, and a workpiece transfer method in which workpieces such as semiconductor wafers from a storage box for storing the workpieces are transferred to a workpiece boat in a workpiece transfer area for heat treatment.
During manufacture of semiconductor integrated circuits such as ICs, LSIs, etc., in general, semiconductor wafers are repeatedly subjected to various processing such as deposition, oxidizing diffusion, etching and the like. In order to perform each processing, the semiconductor wafers needed to be transferred between corresponding devices.
In this case, a plurality of, e.g. 25, semiconductor wafers are transferred while stored in a storage box. Known storage boxes of this type include one such as a cassette transferred while opened to the atmosphere; and another one such as FOUP (trade mark) in which a box is hermetically sealed by an opening-closing lid and filled with an inert gas atmosphere such as a N2 gas atmosphere, or with a clean air atmosphere in order to prevent particles or natural-oxidized films from adhering to semiconductor wafers (see JP-A-8-279546, 9-306975, and 11-274267).
For example, a batch-type processing system for handling the storage box mentioned above generally includes a box transfer area in which the storage box is transferred by a transfer mechanism; and a workpiece transfer area in which semiconductor wafers are transferred from the storage box to a wafer boat or the like for heat treatment (see e.g. JP-A-2002-76089, 2003-37148, and 9-213647). Both the areas are isolated from each other by a partition wall having an opening gate that can be opened and closed to transfer the wafers therebetween. The workpiece transfer area in which the workpieces are transferred while being in a bare state may be brought into an inert gas, e.g. nitrogen atmosphere, or into a clean air atmosphere in order to prevent a natural-oxidized film or the like from adhering to the wafer surfaces.
In the workpiece transfer area, the wafers in the storage box storing e.g. 25 wafers as mentioned above are transferred by use of a wafer transfer mechanism to a wafer boat, a workpiece boat, made of quartz or the like. This can hold a plurality of, e.g. about 50 to 150, wafers in a multistage manner at equal pitches or intervals. After the heat treatment for the wafers has been completed, the wafer is transferred from the wafer boat to the storage box by use of the wafer transfer mechanism reversely to the above in a similar manner.
The known wafer boats made of quartz and generally used in longitudinal thermal treatment equipment include so-called ladder-type wafer boats and so-called ring-type wafer boats (see JP-A-9-213647). Among them, the ladder-type wafer boat is such that struts constituting the wafer boat are formed with wafer support grooves for supporting the edges of wafers. The ring-type wafer boat is such that ringlike tables are spanned between struts in a multistage manner and formed with support claws for supporting the edges of the wafers. Recently, the ring-type wafer boats have tended to be frequently used because of satisfactory gas-flow controllability and relatively satisfactory in-plane uniformity of film thickness.
A transfer mechanism for transferring wafers at high-speed is proposed to meet the request for an improvement in throughput. Specifically, the transfer mechanism proposed has a fork provided with a device for clamping a wafer and transfers the wafer at high speed while clamping the wafer so as not to be displaced on the fork (see e.g. JP-A-2005-286019).
Now, a description is given of a conventional method for transferring wafers to a ring-type wafer boat by use of a wafer transfer mechanism having a clamp device with reference to FIG. 13. Referring to FIG. 13, the wafer boat 2 includes a plurality of ringlike tables 4. The tables 4 are provided on struts not shown so as to be vertically spaced from each other at predetermined pitches P1 in a multistage manner. Each table 4 is provided on an upper surface with e.g. three support claws 6 (only two support claws are shown in the figure). A semiconductor wafer W is placed on the support claws 6.
The fork 8 of the wafer transfer mechanism has a bifurcate end portion and is configured to be movable forward, rearward, upward, and downward. The wafer W is supported on the fork 8. The fork 8 is provided with a stopper member 10 at a distal end. On the other hand, the fork 8 is provided on a proximal end side with clamp means 14 with a pressing portion 12 configured to be movable forward and rearward by e.g. an air cylinder. The wafer W is clamped between the stopper member 10 and the pressing portion 12 so as to be conveyed at high speed in such a state.
For example, if the wafer W on the fork 8 is to be transferred to the wafer boat 2, the wafer W is put and clamped between the pressing portion 12 and the stopper member 10. The fork 8 is inserted between the tables 4 in this state and the pressing portion 12 is slightly moved rearward to release the clamping. The fork 8 is slightly lowered in this state to transfer the wafer W on the fork 8 onto the support claws 6 of the table 4 and thereafter moved rearward.
Incidentally, such batch-type thermal treatment equipment is demanded to further improve throughput. This needs to increase the number of wafers that can be placed on the wafer boat 2 at once. In this case, it is conceivable to increase the height of the wafer boat 2. However, the height of the entire thermal treatment equipment is increased, which undesirably necessitates significant design changes. In contrast, it is conceivable that a pitch P1 between the tables 4 is reduced without changing the height of the wafer boat 2 to increase the number of wafers mountable thereon at once.
If the height of the entire wafer boat 2 is e.g. 1000 mm, 50 wafers W (in terms of finished wafers) can be mounted on the wafer boat 2 at a pitch P1 of 16 mm. If the pitch P1 of the wafer boat 2 is reduced to 11.5 mm, 75 wafers W (in terms of finished wafers) can be mounted so that the number of mountable wafers W can be increased by as many as 25 wafers. Incidentally, the wafer W has a thickness of about 0.7 mm.
In this case, however, the various portions of the wafer transfer mechanism mentioned above are each designed to have significantly marginal dimensions. For this reason, if the wafer W is mounted in the wafer boat 2 with a reduced pitch P1, then the reduced pitch P1 poses a problem in that the pressing portion 12 collides or interferes with an edge portion 4A of a table right above the table 4 on which the wafer W is placed.
In this case, it is conceivable that the thickness or height of the pressing portion 12 is set to such a low level as not to interfere with the upper table. However, it is difficult to change design as mentioned above because the various portions of the wafer transfer mechanism are designed to have significantly marginal dimensions as described above.